This invention relates to a polyarylene sulfide composite material and a process for preparing the composite material. In particular, the invention relates to such a composite material in which a layer-structure silicate mineral material is dispersed in a polyarylene sulfide matrix, said dispersed mineral material being linked to side matrix either by covalent or ionic bonding and relates to a process for preparing the composite material.
Polyarylene sulfides (PAS), typically polyphenylene sulfide (PPS), have been employed in a wide range of applications, for example in production of electronic and electric parts, automobile parts and the like, because of their excellent heat resistance, chemical resistance and fire retardency properties.
However, the PAS materials, in particular PPS that is a crystalline resin, generally have a relatively high glass transition temperature on the order of 90.degree. C. and exhibit a relatively low crystallizing rate. Therefore, where the PAS materials are injection molded to produce moldings, the mold temperature should be set in the range of about 130.degree.-150.degree. C. in order to obtain acceptable products of good heat resistance and dimensional stability properties. Employment of such a high mold temperature has made the PAS materials very disadvantageous where they are used in molding processes, as compared with other engineering plastics, e.g. nylons and PBT, which may be molded with a mold temperature less than 100.degree. C. This is considered to have been a factor arresting expansion of the application of PPS materials.
Further, the PAS materials themselves are brittle and relatively less resistant to heat. Therefore, before use, the materials should incorporate with a reinforcing filler, such as glass fibers or carbon fibers, or inorganic fillers, such as calcium carbonate, mica talc, clay or the like.
However, where the conventional reinforcing fillers are used in a small proportion, the resulting reinforcing effect is not appreciable. Thus, in order to achieve an acceptable reinforcing effect as well as improved thermal resistance and rigidity properties, usually the reinforcing fillers have been required to be used in a proportion as high as about 30-50% by weight. When an inorganic filler, e.g. a clay mineral, is simply added to the PAS materials in accordance with the prior art techniques, the individual silicate layers composing the layer-structure silicate mineral (clay mineral) which strongly interact and adhere to each other could not be brought into a evenly dispersed state in the PAS matrix, but rather would be present as laminates each comprising a large number of silicate layer adhering strongly to each other. Such a difficulty in dispersing the inorganic filler evenly in the resin matrix and hence a correspondingly low reinforcing effect in accordance with the prior art techniques would have necessitated employment of the inorganic fillers in the above-mentioned large proportion. Therefore, the PAS composite materials produced by the conventional techniques have an increased specific gravity that is undesirable for production of lightweight articles or parts. Further, the conventional PAS composite materials loaded with such an increased proportion of inorganic fillers tend to produce moldings having a surface of poor smoothness.
Further, the PAS composite materials achieved by the prior art techniques have another drawback that they show a decreased specific volume resistance under high humidity and temperature conditions, possibly due to a poor affinity between the PAS matrix and the added reinforcing and/or inorganic filler.
When the conventional composite materials loaded with a high proportion of reinforcing filler and/or inorganic filler are used for encapsulating or coating IC devices having very fine bonding wires, there is a risk that the fine wires are accidentally broken or heavily deformed by the solid filler and hence any functional trouble of the IC devices is caused to occur.
In order to solve a relatively low crystallizing rate, various techniques or ideas have been proposed, for example, addition of an oligomeric polyester having a molecular weight of at most 6000 to a PPS of a melt viscosity of at least 5 Pa.s (Japanese Patent Public Disclosure, KOKAI No. 62-45654); addition of a monomeric carboxylate ester (Japanese Patent Public Disclosure, KOKAI No. 62-230848); addition of organic thioethers (Japanese Patent Public Disclosure, KOKAI No. 62-230849); addition of a specific class of aromatic phosphate esters (Japanese Patent Public Disclosure, KOKAI Nos. 62-230850 and, 01-225660). However, these known approaches are effective to promote crystallization of the PAS materials to only a slight extent, but have failed to sufficiently enhance the crystallization to a practically acceptable extent. Since the crystallization-promoting additives proposed in the prior art references are generally of poor thermal resisting properties and tend to volatile or decompose with generating gases during the molding process. Further, since the crystallization-promoting additives are of low molecular weights, the additives tend to migrate to the surface region of product moldings, resulting a smearing problem.
On the other hand, Japanese Patent Public Disclosure, KOKAI No. 62-74957 discloses a composite material of polyamide/layer-structure silicate mineral in which the layer of silicate mineral are evenly distributed in the polyamide resin. In this reference, typically, the layer-structure silicate mineral is organized with an organic onium salt containing carboxyl groups, and the thus resulting organomodified mineral is combined with the polyamide material to give an composite material. However, even though the typical organomodified silicate mineral that was taught in the above-cited reference 62-74957 was combined with a PAS to prepare a PAS-based composite, this composite did not show improved heat resistance and rigidity properties as achieved by the known polyamide/silicate mineral composite materials, since the molecular structure of PAS did exert only a weak affinity for the known modified mineral.
The present invention provides a PAS composite material solving the problems and difficulties experienced with the prior art techniques and which exhibits an increased crystallizing rate and is improved particularly in the heat resistance and rigidity properties. Also, the invention provides a process for preparing such an improved PAS composite material.